“Promising” trial results suggest chikungunya vaccine could be within reach

A phase 3 trial suggests the VLA1553 chikungunya vaccine candidate is safe, well tolerated and provokes strong antibody responses in 99% of recipients.

  • 16 June 2023
  • 4 min read
  • by Linda Geddes
Credit: Chokniti Khongchum on Pexels
Credit: Chokniti Khongchum on Pexels


A vaccine against debilitating chikungunya disease has come a step closer as the results of a large human trial suggest a leading candidate provokes a strong immune response in 99% of participants and is generally well tolerated.

However, because the trial was not conducted in regions where chikungunya is endemic, further studies are needed to prove that it protects against disease and is safe in populations who have already been exposed to the virus.

Chikungunya is a mosquito-borne disease caused by the chikungunya virus, which is endemic in some regions of Africa, Asia, and the Americas. It is rarely fatal, but causes fever and debilitating joint pain, muscle pain, joint swelling, headache, nausea, fatigue and rash. In some patients, the chronic joint pain and other symptoms can persist for months or years. There is currently no approved vaccine or specific treatment for chikungunya virus infections.

Twenty-eight days after receiving a single dose, neutralising antibodies against chikungunya virus were detected at a level that is considered to protect against disease in 99% of those tested.

Valneva's VLA1553 chikungunya vaccine candidate is one of several currently being assessed in phase 3 clinical trials, and the first to report results. It is made from a weakened version of the live chikungunya virus, so is likely to be unsuitable for people with weakened immune systems or during pregnancy.

The new study involved 4,115 healthy adults from across the US. Three-quarters of them were given a single dose of VLA1553 via an injection into their arms, while the rest were given a placebo.

The results, published in The Lancet, suggested that the vaccine was generally well tolerated across all age groups, with most adverse events being mild or moderate. These included headaches, fatigue, muscle or joint pain, and pain at the injection site.

Serious adverse events were reported in 2% (46 out of 3,082) of participants exposed to VLA1553 and 1% (8 out of 1,033) of those who received the placebo. Two of these were classified as related to the vaccine: One was a case of mild muscle pain in a woman with a medical history of fibromyalgia, and the other was a fever, which resulted in hospitalisation. Neither resulted in death.

Immune responses were tested in a subgroup of 266 participants given the VLA1553 vaccine and 96 given the placebo. Twenty-eight days after receiving a single dose, neutralising antibodies against chikungunya virus were detected at a level that is considered to protect against disease in 99% of those tested. There was no difference in immune response according to age.

"This could be the first chikungunya vaccine available for people living in endemic regions, as well as for travellers to endemic areas or areas at risk for an upcoming outbreak," said Dr Martina Schneider, Clinical Strategy Manager at Valneva and the study's lead author. "Our promising results showed good persistence of antibody levels after vaccination, which is important considering that chikungunya outbreaks may recur suddenly. As age is a risk factor for severity and mortality of chikungunya disease, the strong immune response observed in older participants might be particularly beneficial."

Dr Kathryn Stephenson, an infectious disease expert at the Beth Israel Deaconess Medical Center in Boston, US, who was not involved in the study, hailed the results as a possible "new era" in the development of vaccines against chikungunya virus.

Writing in a linked commentary she said: "The positive results of this trial are good news for chikungunya virus pandemic preparedness. Chikungunya virus and other arboviral infections continue to be global threats, spurred on by the expansion of mosquito habitats because of climate change and globalisation of trade and travel.

"Further studies of VLA1553 in endemic regions and expanded populations, such as an ongoing trial in adolescents in Brazil, will be crucial to affirming VLA1553's value for chikungunya virus prevention, as will be real-world effectiveness studies in the context of actual chikungunya virus outbreaks."

However, she stressed that there are also downsides to using live-attenuated vaccines such as VLA1553. Besides typically being unsuitable for people with weakened immune systems or pregnant individuals, manufacturing usually involves growing large quantities of live virus in highly contained and secure facilities.

Live vaccines are also sensitive to heat and may be more difficult to store and ship, than other types of vaccine, Stephenson said. For these reasons, other candidates such as adjuvanted virus-like particle vaccines and inactivated vaccines should also continue to be developed.